Tanks for use in storing low temperature liquefied gas

ABSTRACT

Tank for use in storing low temperature liquefied gas comprising a rigid outer vessel, a thin film inner vessel with rigid partition walls, and a heat insulating layer inserted between these two vessels. Each of the partition walls extends through the inner vessel and is slidably supported by the outer vessel to permit expansion and contraction of the partition walls. The thin film inner vessel walls are secured to the partition walls at points near where the partition walls pass into the heat insulating layer to form a closed vessel having a large capacity.

[56] References Cited UNITED STATES PATENTS 2 953 6/1959 Morrison...................... 3 769 6/1962 Smith............ 3 794 9/1964 Schlumberger et al. 3 795 9/ 1964 Schlumberger 3 4/1967 Becker et al...... l/1969 Bridges etal. Primary Examiner-Joseph R. Leclair Assistant Examiner-James R. Garrett Attorney-Holman & Stern Katsuro Yamaoto Tokyo, Japan 780,649 Dec. 3, 1968 [45] Patented Mar.l6, 1971 Bridgestone Liqueiied Petroleum Gas Company Limited Tokyo, Japan Dec. 26, 1967 Japan 42/82933 large capacity.

TANKS FOR USE IN STORING LOW TEMPERATURE LIQUEFHED GAS This invention relates to tanks for use in storing methane, propane, butane etc. in liquid phase. Such materials are gaseous state' at room temperature under atmospheric pressure, but can be liquefied by cooling to their boiling point under atmospheric pressure.

It is particularly applicable to tanks for use in tankers for transporting the low temperature liquefied gas.

lt has been well known that two different types of tanks for use in tankers for transporting low temperature liquefied gas are available, i.e. an independent type tank and a thin film type tank.

The thin film type tank is constructed such that a wall in contact with the liquefied gas is made of a plate-shaped fiexi ble thin film and that the inner pressure produced in the tank is supported through a compression resistant heat insulating layer by a hull constructional member. Such thin film-type tank has advantages over the independent type tank in which tanks are provided independently in the hull, but has a number of difficulties which must be overcome.

One of such difficulties with thin film type tanks consists in the provision of partition walls in the tank. An inboard tank must be divided into a plurality of spaces to store the liquefied gas separately for the purpose of preventing the liquefied gas from being subjected to the rocking motion of the ship. This is required for the sake of keeping the ship in a stable state. Thus, the partition walls must withstand shocks resulting from the rocking motion of the liquefied gas charged in the tank and hence must be of a rigid construction. ln the thin film-type tank it is difficult to secure these rigid partition walls to the flexible inner vessel for the following reasons. The rigid partition walls are contracted when exposed to the low temperature liquefied gas and move that part of the thin film portion which is secured to the partition walls from the heat insulating layer, with the result that a gap is formed between said part of the thin film portion and the heat insulating layer. With the thin film portion separated from the heat-insulating layer it can not be supported by the latter and hence can not withstand the liquefied gas pressure. Moreover, there is a risk that stresses will be concentrated at joints between the rigid partition walls and the flexible thin film portion. In order to avoid such such risk in the conventional thin film type tanks it is necessary to divide the hull into a large number of spaces each containing a thin film type tank having a small capacity and not provided with partition walls. Such conventional tank has the disadvantages that a space in the hull cannot be utilized effectively, that the amount of cargo is decreased and that the manufacturing cost of the liquefied gas transporting ship becomes expensive.

The principal object of the invention is to obviate the above-mentioned disadvantages and provide a thin film-type tank for use in storing low temperature liquefied gas that is capable of providing partition walls and containing in the hull a small number of tanks each having a large capacity.

For a better understanding of the invention, reference is taken to the accompanying drawings, wherein:

FIG. 1 is a transverse sectional view of a low temperature liquefied gas according to the invention;

FIG. 2 is a section on line A-A of FIG. 1, parts being broken away;

FIGS. 3 and 4 diagrammatically illustrate the construction of inner vessels of a tank according to the invention; and

FIG. 5 is a partial section of another embodiment of a tank according to the invention.

Referring now to FIGS. 1 and 2 there are shown transverse and longitudinal sections of a tank according to the invention comprising an outer vessel 1, a heat insulating layer 2 provided in the inside surface of the outer vessel 1 and an inner vessel 3 provided inside of the heat insulating layer 2. The inner vessel 3 is constructed such that it cannot withstand the inner pressure produced therein, the detailed construction of which will hereinafter be described. The outside surface of the inner vessel 3 is urged against the heat insulating layer 2 by means of the inner pressure producedin the inner vessel 3. This inner pressure is supported through the heat insulating layer 2 by the outer vessel l which has a rigid construction. ln case of an inboard tank the outer vessel 1 constitutes a hull structural member.

As above-mentioned the heat insulating layer 2 serves to transmit the inner pressure produced in the inner vessel 3 to the outer vessel 1 so that the heat insulating layer 2 must be of a pressure resisting construction. The heat insulating layer 2 may be constructed by a heat insulating material having a compression resistant property or by a composite material consisting of a heat insulating material having a compressive property and a heat insulating material having a compression resistant property such as wood etc. In the latter case the inner pressure produced in the inner vessel 3 may be transmitted through that portion consisting of the heat insulating material having the compression resistant property to the outer vessel l.

The inner vessel 3 comprises a wall portion having a thinfilm construction, that is, a thin film portion 4 and partition walls 5, 6 each having a rigid construction. 5 designates a transverse partition wall extending along the hull in a transverse direction and 6 a longitudinal partition wall extending along the hull in a longitudinal direction. The inner vessel 3 need not always include both the transverse partition wall 5 and the longitudinal partition wall 6. Provision may be made of either one of these two partition'walls. The partition walls 5, 6 divide the space surrounded by the heat insulating layer 2 into a plurality of spaces. The outer peripheral edges 5', 6 of the partition walls 5, 6 terminate in the heat insulating layer 2.

The thin film portion 4 is arranged along the inside surface of the heat insulating layer 2 and covers all of the inside surface of the heat insulating layer 2 in a fluidtight manner. The thin film portion 4 as a whole does not constitute a single continuous wall of the inner vessel 3, but is divided into separate thin film portions by means of the partition walls 5, 6. For example, in the embodiment shown in FIG. l the thin film portion 4 is divided into four separate thin film portions 4a, 4b, 4c and 4d. Each of these separate thin film portions, for example, the portion 4a constitutes a cube consisting of two side surfaces 7, 8, a top surface 9, a bottom surface 10 and two open side surfaces l1, l2 as shown in FIG. 3. These open side surfaces 11, 12 are closed by the partition walls 5 and 6, respectively, to form a closed cube. The separate thin film portion 4a is welded along its peripheral edges surrounding the open side surfaces l1, 12 to the partition walls 5, 6.

FIG. 4 shows similarly to FIG. 3 an inner vessel provided with one partition wall, in which 13 designates a partition wall having a rigid construction and 14 a thin film portion having only one open surface closed by the partition wall 13.

The peripheral edges 5, 6 of the partition walls 5, 6 terminate in the heat insulating layer 2 and are slidably supported by means of key members 15, 1S made of wood etc. and secured to the outer vessel 1. Thus, the partition walls 5, 6 can freely expand and contract in response to temperature changes. The impact force acting transversely upon these partition walls 5, 6 can be transmitted through the key members 15, 15 to the rigid outer vessel 1. The liquid pressure acting upon the thin film portion is transmitted through the heat insulating layer 2 to the outer vessel 1.

As explained hereinbefore the in use of the inner vessel having the thin film construction and provided with the rigid partition walls provides the important advantage that there is no need to provide a number of thermally insulated small chambers in the hull and accommodating a thin film-type inner ves sel having a small capacity in each of these small chambersas in the conventional low temperature liquefied gas transporting ship having the thin film tank construction, that the hull may be divided into large spaces and inner vessels each having a large capacity may be accommodated in these large spaces thus reducing the construction cost, and that the space in the hull can effectively be used as a cargo space.

The thin film portion 4 of the inner vessel 3 is adapted to be deflected .when subjected to the inner pressure produced in the inner vessel 3 and brought into contact with the inside surface of the heat insulating layer 2. The thin film portion 4 per se could not maintain its configuration so that its top surface 9 is suspended from the top wall of the outer vessel l. In FIG. 2, 16 designates a reinforcing member for suspending the top surface 9 and 17 which is a hanging device. This hanging device 17 is constructed such that the top surface 9 is capable of effecting expansion and contraction, that is, the top surface 9 is movable in a horizontal direction.

Eighteen designates vertical corrugations formed in parallel and spaced one from the other along the side surfaces of the thin film portion 4. If the inner vessel 3 is charged with the low temperature liquefied gas, the wall of the inner vessel 3 becomes contracted and the wall thus contracted is urged against the heat insulating layer 2 by means of the inner pressure produced in the inner vessel 3, so that the inner vessel is subjected to a tensile stress. In this case, the corrugations 18 are elongated and reduce the tensile stress to substantially zero. In case of urging the thin filmportion 4 against the heat insulating layer 2 by means of the inner pressure produced in the inner vessel 3, if the corrugations 18 remain in more or less extent, then compressive stress, instead of the tensile stress, is produced in the thin film portion. Thus, there is no fear of breaking off the thin film portion 4 by, tension. Thus, the vertical corrugations 18 serve to absorb expansion and contraction of the inner vessel 3 in its horizontal section.

As above mentioned, the top surface 9 of the thin`film portion 4 is suspended from the top wall of the outer vessel 1 so that the top surface 9 is not permitted to move in vertical direction. A bottom surface l of the thin film portion 4 is always kept in contact with the heat insulating layers 2. Thus, it is necessary to provide means of absorbing expansion and contraction of the two side surfaces 7, 8 of the thin film portion 4 in a vertical direction and absorbing expansion and contraction of its top and bottom surfaces 9, l0 in a horizontal direction. For this purpose, the upper and lower edges of each side surface 7 or 8 may be secured through curved portions to the top and bottom surfaces 9 and 10, respectively. The curvature of these curved portions may be varied so as to absorb the expansion and contraction of the side surfaces 7, 8, top surface 9 and bottom surface l0. Alternatively, the top and bottom surfaces 9 and 10 may be provided with suitable corrugations.

As above-mentioned, the peripheral edges 6' of the partition walls 5, 6 are slidably supported by means of the key members 15, as shown in FIGS. 1, 2 and 5. lf the partition walls 5, 6 become contracted when exposed to the low temperature liquefied gas, their upper edges move downwards. In this case a joint 19 between the top surface 9 of the thin film portion 4 and the partition wall 5 also moves downwards to bend a part of the top surface 9 to a position shown by dotted lines 20 in FIG. 2. That is, the contraction of the partition wall 5 causes to bend that portion 20 of the top surface 9 which is adjacent to the partition wall 5. Joints between the side surfaces 7, 8 and the partition walls 5, 6, respectively, also move in a manner similar to that explained above with reference to the joint 19.

The bent portion 20 which is separated from the heat insulating layer 2 must support directly the pressure of the low temperature liqueed gas. For this reason, the part of the thin film portion 4 which is adjacent to the partition wall is made more rigid than other part as shown at 21 in FIG. l. The longer the distance from the partition wall, the deflection of the thin film portion becomes larger and finally the thin film comes in contact with the heat insulating layer 2. ln the embodiments shown in FIGS. 1 4, the thin film portion 4 is directly secured to the partition walls 5, 6, but in the embodiment shown in FIG. 5 thin film portion 4 is secured through a curved portion 22 to the partition walls 5, 6. In the embodiment shown in FIG. 5 if the partition wall 5 becomes contracted when exposed to the low temperature liq uefied gas the curved portion 2 moves to a position shown y dotted lines 22'. Thus, the

inner pressure produced in the inner vessel 3 acting upon this curved portion 22' can be supportedby the tension produced therein.

As explained hereinbefore the use of the inner vessel made of a thin film and provided with rigid partition walls ensures provision of a small number of thin film-type tanks each having a large capacity in a hull and further provides the important advantages that a space in the hull can effectively be utilized, the amount of cargo can be increased and that a low temperature liquefied gas transporting ship can be manufactured in a less expensive manner.

As seen from the above, the thin film portion of the inner vessel according to the invention is supported not only by the top surface, but also by the partition walls. As a result of this, the additional advantage is obtained that the thin film portion cannot be moved as a whole, and that the configuration of the thin film portion cannot be deformed. If a bag-shaped thin film portion is suspended from the top wall of the outer vessel through the top surface only of the thin film portion, there is risk of the curved portions formed between the top surface and the side surfaces being repeatedly deformed by the rocking motion of the ship and the low temperature liquefied gas.

It will be obvious that the invention is not restricted to the examples described and that many variations are possible to those skilled in the art without departing from the scope of this invention.

Iclaim:

1. A tank for use in storing low temperature liquefied gas comprising, in combination, an outer vessel having a rigid construction, a heat insulating layer provided on the inside surface of said outer vessel and an inner vessel provided inside of said insulating layer, said inner vessel having walls of thin film construction which are capable of being deflected by the pressure produced by the low temperature liquefied gas in said inner vessel and brought into a close contact with said heat insulating layer so that said pressure is supported through said heat insulating layer by said rigid outer vessel, and partition wall means of impervious material provided in said inner vessel to divide said inner vessel into a plurality of spaces, said partition wall means extending transversely of said inner vessel and through said walls of thin film construction into said heat insulating layer and being supported by said outer vessel with the expansion and contraction of said partition wall means being accommodated, said walls of thin film construcn tion being tightly sealed to said partition wall means so as to form a closed vessel in each of said plurality of spaces in cooperation with said partition wall means. 

